FIG. 1 illustrates a prior art DC-DC converter that utilizes a boost converter followed by a voltage multiplier stage to step up the voltage available from a power source. The boost converter 10 includes an input inductor LIN that receives power from an input voltage source VIN, and a transistor switch S coupled to the inductor LIN at a switching node NS. The voltage multiplier stage 12 includes two diodes DM1 and DM2 connected in series between the switching node NS and a boost node NB. A multiplier stage capacitor CM1 is coupled to an intermediate node NI between the diodes DM1 and DM2. A resonant inductor LR and capacitor CM2 are connected in series between the switching node NS and the boost node NB and impart a quasi-resonant characteristic to the multiplier stage. The converter of FIG. 1 also includes an output or filter stage 14 having another diode DO, as well as an output capacitor CO. The output load is shown as a load resistor RO.
With proper tuning, the quasi-resonant characteristics of the multiplier stage reduce the maximum voltage across the transistor switch S, as well as enable it to operate with zero current switching (ZCS). Both of these characteristics reduce stress on the switch, thereby improving reliability and reducing its cost. These characteristics also enable the use of lower voltage switching devices which reduces the on-state resistance of the devices, thereby reducing switching losses and enabling the converter to operate at higher frequencies.
A single multiplier stage, however, may not provide adequate voltage gain for many applications. Therefore, additional voltage multiplier stages may be added as shown in FIG. 2, which illustrates a generalized converter having a boost stage 10 followed by a total of M multiplier stages 12-1, 12-2, . . . 12-M. Each multiplier stage includes two diodes and two capacitors. Only the first stage is shown with a resonant inductor LR, but additional inductors could be connected in series with capacitors C22 . . . CM2 in the successive stages as well. The additional multiplier stages increase the voltage gain of the converter by a factor of M+1, which theoretically increases the output voltage by factor of (M+1) times the maximum switch voltage.